Electronic device cooling system with storage

ABSTRACT

Cooling systems for providing cooled air to electronic equipment are described. The systems can include large storage tanks or waste treatment systems to improve the efficiency of the plant and reduce impact on the environment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser.No. 61/016,419, filed on Dec. 21, 2007.

TECHNICAL FIELD

This document relates to systems and methods for providing cooling forareas containing electronic equipment, such as computer server rooms andserver racks in computer data centers.

BACKGROUND

Computer users often focus on the speed of computer microprocessors(e.g., megahertz and gigahertz). Many forget that this speed often comeswith a cost—higher electrical power consumption. For one or two homePCs, this extra power may be negligible when compared to the cost ofrunning the many other electrical appliances in a home. But in datacenter applications, where thousands of microprocessors may be operated,electrical power requirements can be very important.

Power consumption also, in effect, creates a double hit. Not only must adata center operator pay for electricity to operate its many computers,but the operator must also pay to cool the computers. That is because,by simple laws of physics, all the power has to go somewhere, and thatsomewhere is, for the most part, conversion into heat. A pair ofmicroprocessors mounted on a single motherboard can draw 200-400 wattsor more of power. Multiply that figure by several thousand (or tens ofthousands) to account for the many computers in a large data center, andone can readily appreciate the amount of heat that can be generated. Itis much like having a room filled with thousands of burning floodlights.

Thus, the cost of removing all of the heat can also be a major cost ofoperating large data centers. That cost typically involves the use ofeven more energy, in the form of electricity and natural gas, to operatechillers, condensers, pumps, fans, cooling towers, and other relatedcomponents. Heat removal can also be important because, althoughmicroprocessors may not be as sensitive to heat as are people, increasesin heat generally can cause great increases in microprocessor errors andfailures. In sum, such a system may require electricity to run thechips, and more electricity to cool the chips.

SUMMARY

This document describes systems and methods that may be employed toremove heat efficiently from areas hosting electronic equipment, such asdata centers. In certain implementations, cooling of equipment may occurat elevated air temperatures. For example, high temperature rises may becreated across a group of heat-generating components by intentionallyslowing the flow of cooling air over the components. As one example,temperature rises across the components of thirty-six degrees Fahrenheit(twenty degree Celsius) or more may be maintained, with entering airtemperatures of about seventy-seven degrees Fahrenheit (twenty-fivedegrees Celsius) and exiting temperatures of about one hundred thirteendegrees Fahrenheit (forty-five degrees Celsius). The temperatures of anyassociated cooling water may also be elevated, such as to produce supplytemperatures of about sixty-eight degrees Fahrenheit (twenty degreesCelsius) and return temperatures of about one hundred four degreesFahrenheit (forty degrees Celsius). Because of the elevatedtemperatures, the system may be run under most conditions using onlycooling from cooling towers or other free cooling sources, without theneed for a chiller or other similar sources that require additionalpower for cooling.

In one embodiment, a system for providing cooled air to electronicequipment is described. The system has a cooling tower, a water storagetank fluidly coupled to the cooling tower and an air-to-water heatexchanger thermally connected to the water storage tank and positionedto receive heated air from a group of electronic devices.

In another embodiment, a method of providing cooled air to electronicequipment is described. Water in a cooling tower is allowed to coolthrough evaporative cooling. Water is flowed from the cooling tower to awater storage tank. Water is flowed from the water storage tank to anair-to-water heat exchanger. The water flowing through the air-to-waterheat exchanger cools air surrounding the heat exchanger that has beenheated by a group of electronic devices.

In yet another embodiment, a method of providing cooled air toelectronic equipment is described. Water in a cooling tower is allowedto cool through evaporative cooling. Water is flowed from the coolingtower to a water storage tank. Water is flowed from the water storagetank to a water-to-water heat exchanger. Water is flowed from thewater-to-water heat exchanger through an air-to-water heat exchanger.The water flowing through water-to-air heat exchanger is kept isolatedfrom the water from the water storage tank and is flowed through theair-to-water heat exchanger to cool air surrounding the heat exchangerthat has been heated by a group of electronic devices.

In another embodiment, a system for providing cooled air to electronicequipment is described. The system includes a cooling tower, a watertreatment system fluidly coupled to the cooling tower and anair-to-water heat exchanger connected by a pair of pipes to the coolingtower and positioned to receive heated air from a group of electronicdevices.

In yet another embodiment, a method of providing cooled air toelectronic equipment is described. Water in a cooling tower is allowedto cool through evaporative cooling. Water from the cooling tower isflowed to an air-to-water heat exchanger, wherein the water flowingthrough the air-to-water heat exchanger cools air surrounding the heatexchanger that has been heated by a group of electronic devices. Waterheated by the air surrounding the heat exchanger is flowed into thecooling tower. Water is flowed from the cooling tower into a watertreatment system for removing impurities from the water.

In another embodiment, a system for providing cooled air to electronicequipment is described. The system includes a source of non-potablewater, a cooling tower in fluid communication with the source ofnon-potable water, and an air-to-water heat exchanger thermallyconnected to the cooling tower and positioned to receive heated air froma group of electronic devices.

In yet another embodiment, method of providing cooled air to electronicequipment is described. Non-potable water is provided to a coolingtower. Water in the cooling tower is allowed to cool through evaporativecooling. Water is flowed from the cooling tower to an air-to-water heatexchanger, wherein the water flowing through the air-to-water heatexchanger cools air surrounding the heat exchanger that has been heatedby a group of electronic devices.

In another embodiment, a system for providing cooled air to electronicequipment is described. The system includes a water storage pond, areflective cover on the storage pond, a water treatment system fluidlycoupled to the storage pond and an air-to-water heat exchanger connectedto the water treatment system and positioned to receive heated air froma group of electronic devices.

In yet another embodiment, a method of providing cooled air toelectronic equipment. Water is provided to a water storage pond. Waterin the storage pond is allowed to cool through evaporative cooling.Water is flowed from the storage pond to a water treatment system andimpurities are removed from the water at the water treatment system.Water is flowed from the water treatment system to an air-to-water heatexchanger, wherein the water flowing through the air-to-water heatexchanger cools air surrounding the heat exchanger that has been heatedby a group of electronic devices.

In another embodiment, a modular system for providing cooling water to abuilding housing a group of electronic devices includes a module and awater storage. The module includes a housing, wherein the housing is nomore than 13.5 feet wide and is no longer than 97 feet, a water-to-waterheat exchanger within the housing, a chiller within the housing and acontroller within the housing, wherein the controller regulates a flowof water from the water-to-water heat exchanger and the chiller tooutside of the housing. The water storage tank has a capacity of atleast 10,000 gallons and is fluidly coupled to at least one of thechiller and the water-to-water heat exchanger.

Advantages of the systems and methods described herein may include oneor more of following. Recirculation of water through a cooling systemcan decrease the system's reliance on municipal or county water sources.This may both reduce the cost of operation of the cooling system, aswell as benefit the local municipality. The municipality's resources arenot as heavily drawn upon by the cooling system as with other types ofwater based cooling systems, such as systems that run tap water into thesystem and straight in to the sewer after the water has been used.Further, a system as described herein can reduce the load upon the localsewer system and sewage treatment plant, as only a fraction of the waterused by the cooling system may be released into the sewage system eachday. An optional on-site water treatment facility may further reduce theload on the local sewage system. The on-site water treatment facilitymay be used to treat water coming into the system that is not as cleanas needed and may even provide environmental benefits of cleaning waterthat would normally not be treated, and later returning the water to theenvironment cleaner than when it was removed. If the cooling systemincludes a storage tank, the storage tank can provide a source of waterfor cooling in the event the regularly available water is out of servicefor some period of time, such as for up to a day or a few days. Further,the cooling system can provide massive storage that may be able tocompensate for any air temperature peaks and troughs that occur oversome period of time, such as over a day or over a few days. The tanksystem may also reduce the need for chillers to chill the water, whichin turn can reduce the amount of electricity required by a coolingplant. The use of less electricity may enable locating the coolingsystem in a greater variety of locations than a system that has highelectrical needs. A cooling system with lower electrical needs may beboth more cost efficient to operate and have a lower environmentalimpact than more energy intensive plants. The cooling system can bemodularized. This can allow for construction of complex piping andwiring to be performed in a controlled environment, such as a factory,rather than on-site. Controlled build conditions can increaserepeatability and decrease construction problems. The modules alsoenable a data center to be built at a particular capacity and expandedto greater capacity as the need for more electronic equipment, such asservers, grows. Further, this allows for scaling the cost of buildingthe data center to the current needs of the data center, while leavingroom for future growth.

The details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram showing a system for cooling a computerdata center.

FIG. 2 is a schematic diagram showing a system for cooling a computerdata center.

FIG. 3A is a psychometric chart showing a heating and cooling cycle forair in a data center.

FIG. 3B is a graph of setpoint temperature for a computing facility overa one year time period.

FIG. 4 is a plan view in schematic form of a hydronic cooling system fora data center.

FIG. 5 is a plan view in schematic form of a hydronic cooling system fora data center housed in shipping containers.

FIG. 6 is a flowchart showing steps for cooling a data center usingelevated temperatures.

FIG. 7A is a schematic diagram showing a system for cooling a computerdata center.

FIG. 7B is a flowchart showing the steps for routing water through thecooling system.

FIG. 8 is a schematic diagram including a settling pond.

FIG. 9 is a schematic diagram of a data center with one modularizedcooling system.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

FIG. 1 is a schematic diagram showing a system 100 for cooling acomputer data center 101. The system 100 generally includes an airhandling unit (including e.g., fan 110 and cooling coils 112 a, 112 b)in the data center 101 for transferring heat from the data center's airto cooling water, a heat exchanger 122 for removing heat from thecooling water and passing it to cooling tower water, and a cooling tower118 to pass the accumulated heat to the ambient air through evaporationand cooling of the cooling tower water. In general operation, the system100 may be run from the cooling tower/heat exchanger/cooling coilsystem, though a powered refrigeration system such as a chiller may beprovided for peak loads, such as when the outdoor ambient dew point isvery high and the cooling tower cannot provide sufficient cooling alone.As explained below, control parameters for the system may also be set soas to avoid most or any need for the use of chillers or other suchitems.

The temperatures of each portion of the system 100 are selected to berelatively high, so as to permit more efficient operation of the system100, than if the temperatures were lower. For example, relatively highair temperatures in the system (e.g., air entering a cooling coil over110° F. (43.3° C.) and exiting temperature above 70° F. (21.11° C.)) mayin turn permit for relatively high cooling water temperatures (e.g.,water entering a cooling coil around 68° F. (20° C.) and exiting around104° F. (40° C.)) because the amount of heat that can be taken out ofthe air is generally proportional to the difference in temperaturebetween the water and the air. If the difference can be kept at anacceptable level, where the temperatures are high enough thatevaporative cooling (e.g., cooling through a cooling tower, withoutfurther cooling via chiller) is sufficient, the relatively highelectrical cost of operating a chiller (or many chillers) may beavoided.

High system temperatures may be particularly advantageous in certainimplementations when hybrid cooling towers are used. Such hybrid coolingtowers combine the functionality of an ordinary cooling tower with awater-to-water heat exchanger. Sufficiently high chosen temperaturesetpoints may allow the hybrid tower to provide substantial coolingcapacity, even when operating in a water-to-air mode without utilitywater. As a result, a hybrid cooling tower may be used to providecooling capacity to a facility relatively quickly, even before utilitywater may be obtained in large volumes. The capacity of the coolingtower may be directly related to the difference in the temperature ofthe water within it to the ambient outside air.

When the difference in temperatures is not very large, a change of onlya few degrees can bring substantial gains in efficiency. For example,where the cooling water enters at 68° F. (20° C.), by heating air to113° F. (45° C.) rather than 104° F. (40° C.), the temperaturedifference is increased from 36° F. to 45° F. (2° C. to 7° C.)—which mayresult in an increase in heat flow of 25 percent. The actual differencewill vary slightly, as the entering conditions for air and water are notthe only conditions (because the air cools as it passes through acooling coil, and the water warms); this example, however, indicates howthe difference in temperature can affect efficiency of a system.

Use of elevated temperatures in a system may also prevent air in oraround the system from falling below its liquid saturation point, i.e.,its dew point, and condensing. This may, in certain circumstances,provide benefits both in efficiency and in operations of the system.Efficiency benefits may be obtained because creating condensationrequires much more energy than simply cooling air, so that systemscreating condensation may use a large amount of electricity or otherenergy. Improvements in operations of the system may occur because, ifpipes in the system carry water that is below the saturation temperatureof the air around the pipes, condensation might form on the pipes. Thatcondensation can damage the pipes or equipment in the conditioned space,cause mold, and cause water to pool on the floor, and can require theinstallation of insulation on the pipes (to stop the condensation).

In the system shown in FIG. 1, use of elevated temperatures maysubstantially reduce, or almost entirely eliminate, the need forenergy-intensive cooling components such as chillers and the like, evenwhere the heat load in the data center 101 is very high. As a result,system 100 may be operated at a lower operating cost than couldotherwise be achieved. In addition, lower capital costs may be required,because fans, coils, heat exchangers, and cooling towers are relativelybasic and inexpensive components. In addition, by operating with ahigher temperature difference between cooled air and cooling water, lessvolume of cooling water is needed, thus reducing the size and cost ofpiping, and the cost to operate pumps and other such components.

In addition, those components are often very standardized, so that theiracquisition costs are lower, and they are more easily located,particularly in developing countries and remote areas where it may bebeneficial to place a data center 101. Use of system 100 in remote areasand other areas with limited access to electrical power is also helpedby the fact that system 100 may be operated using less electrical power.As a result, such a system can be located near lower-power electricalsub-stations and the like. As discussed more completely below,lower-powered systems may also be amenable to being implemented asself-powered systems using energy sources such as solar, wind,natural-gas powered turbines, fuel cells, and the like.

A data center 101 in sectional view is a building that houses a largenumber of computers or similar heat-generating electronic components. Aworkspace 106 is defined around the computers, which are arranged in anumber of parallel rows and mounted in vertical racks, such as racks 102a, 102 b. The racks may include pairs of vertical rails to which areattached paired mounting brackets (not shown). Trays containingcomputers, such as standard circuit boards in the form of motherboards,may be placed on the mounting brackets.

In one example, the mounting brackets may be angled rails welded orotherwise adhered to vertical rails in the frame of a rack, and traysmay include motherboards that are slid into place on top of thebrackets, similar to the manner in which food trays are slid ontostorage racks in a cafeteria, or bread trays are slid into bread racks.The trays may be spaced closely together to maximize the number of traysin a data center, but sufficiently far apart to contain all thecomponents on the trays and to permit air circulation between the trays.

Other arrangements may also be used. For example, trays may be mountedvertically in groups, such as in the form of computer blades. The traysmay simply rest in a rack and be electrically connected after they areslid into place, or they may be provided with mechanisms, such aselectrical traces along one edge, that create electrical and dataconnections when they are slid into place.

Air may circulate from workspace 106 across the trays and into warm-airplenums 104 a, 104 b behind the trays. The air may be drawn into thetrays by fans mounted at the back of the trays (not shown). The fans maybe programmed or otherwise configured to maintain a set exhausttemperature for the air into the warm air plenum, and may also beprogrammed or otherwise configured to maintain a particular temperaturerise across the trays. Where the temperature of the air in the workspace 106 is known, controlling the exhaust temperature also indirectlycontrols the temperature rise. The work space 106 may, in certaincircumstances, be referenced as a “cold aisle,” and the plenums 104 a,104 b as “warm aisles.”

The temperature rise can be large. For example, the work space 106temperature may be about 77° F. (25° C.) and the exhaust temperatureinto the warm-air plenums 104 a, 104 b may be set to 113° F. (45° C.),for a 36° F. (20° C.)) rise in temperature. The exhaust temperature mayalso be as much as 212° F. (100° C.) where the heat generating equipmentcan operate at such elevated temperature. For example, the temperatureof the air exiting the equipment and entering the warm-air plenum may be118.4, 122, 129.2, 136.4, 143.6, 150.8, 158, 165, 172.4, 179.6, 186.8,194, 201, or 208.4° F. (48, 50, 54, 58, 62, 66, 70, 74, 78, 82, 86, 90,94, or 98° C.). Such a high exhaust temperature generally runs contraryto teachings that cooling of heat-generating electronic equipment isbest conducted by washing the equipment with large amounts offast-moving, cool air. Such a cool-air approach does cool the equipment,but it also uses lots of energy.

Cooling of particular electronic equipment, such as microprocessors, maybe improved even where the flow of air across the trays is slow, byattaching impingement fans to the tops of the microprocessors or otherparticularly warm components, or by providing heat pipes and relatedheat exchangers for such components.

The heated air may be routed upward into a ceiling area, or attic 105,or into a raised floor or basement, or other appropriate space, and maybe gathered there by air handling units that include, for example, fan110, which may include, for example, one or more centrifugal fansappropriately sized for the task. The fan 110 may then deliver the airback into a plenum 108 located adjacent to the workspace 106. The plenum108 may be simply a bay-sized area in the middle of a row of racks, thathas been left empty of racks, and that has been isolated from anywarm-air plenums on either side of it, and from cold-air work space 106on its other sides. Alternatively, air may be cooled by coils defining aborder of warm-air plenums 104 a, 104 b and expelled directly intoworkspace 106, such as at the tops of warm-air plenums 104 a, 104 b.

Cooling coils 112 a, 112 b may be located on opposed sides of the plenumapproximately flush with the fronts of the racks. (The racks in the samerow as the plenum 108, coming in and out of the page in the figure, arenot shown.) The coils may have a large surface area and be very thin soas to present a low pressure drop to the system 100. In this way,slower, smaller, and quieter fans may be used to drive air through thesystem. Protective structures such as louvers or wire mesh (not shown)may be placed in front of the coils 112 a, 112 b to prevent them frombeing damaged.

In operation, fan 110 pushes air down into plenum 108, causing increasedpressure in plenum 108 to push air out through cooling coils 112 a, 112b. As the air passes through the coils 112 a, 112 b, its heat istransferred into the water in the coils 112 a, 112 b, and the air iscooled.

The speed of the fan 110 and/or the flow rate or temperature of coolingwater flowing in the cooling coils 112 a, 112 b may be controlled inresponse to measured values. For example, the pumps driving the coolingliquid may be variable speed pumps that are controlled to maintain aparticular temperature in work space 106. Such control mechanisms may beused to maintain a constant temperature in workspace 106 or plenums 104a, 104 b and attic 105.

The workspace 106 air may then be drawn into racks 102 a, 102 b such asby fans mounted on the many trays that are mounted in racks 102 a, 102b. This air may be heated as it passes over the trays and through powersupplies running the computers on the trays, and may then enter thewarm-air plenums 104 a, 104 b. Each tray may have its own power supplyand fan, with the power supply at the back edge of the tray, and the fanattached to the back of the power supply. All of the fans may beconfigured or programmed to deliver air at a single common temperature,such as at a set 113° F. (45° C.). The process may then be continuouslyreadjusted as fan 110 captures and circulates the warm air.

Additional items may also be cooled using system 100. For example, room116 is provided with a self-contained fan-coil unit 114 which contains afan and a cooling coil. The unit 114 may operate, for example, inresponse to a thermostat provided in room 116. Room 116 may be, forexample, an office or other workspace ancillary to the main portions ofthe data center 101.

In addition, supplemental cooling may also be provided to room 116 ifnecessary. For example, a standard roof-top or similar air-conditioningunit (not shown) may be installed to provide particular cooling needs ona spot basis. As one example, system 100 may be designed to deliver 78°F. (25.56° C.) supply air to work space 106, and workers may prefer tohave an office in room 116 that is cooler. Thus, a dedicatedair-conditioning unit may be provided for the office. This unit may beoperated relatively efficiently, however, where its coverage is limitedto a relatively small area of a building or a relatively small part ofthe heat load from a building. Also, cooling units, such as chillers,may provide for supplemental cooling, though their size may be reducedsubstantially compared to if they were used to provide substantialcooling for the system 100.

Fresh air may be provided to the workspace 106 by various mechanisms.For example, a supplemental air-conditioning unit (not shown), such as astandard roof-top unit may be provided to supply necessary exchanges ofoutside air. Also, such a unit may serve to dehumidify the workspace 106for the limited latent loads in the system 100, such as humanperspiration. Alternatively, louvers (not shown) may be provided fromthe outside environment to the system 100, such as powered louvers toconnect to the warm air plenum 104 b. System 100 may be controlled todraw air through the plenums when environmental (outside) ambienthumidity and temperature are sufficiently low to permit cooling withoutside air. Such louvers may also be ducted to fan 110, and warm air inplenums 104 a, 104 b may simply be exhausted to atmosphere, so that theoutside air does not mix with, and get diluted by, the warm air from thecomputers. Appropriate filtration may also be provided in the system,particularly where outside air is used.

Also, the workspace 106 may include heat loads other than the trays,such as from people in the space and lighting. Where the volume of airpassing through the various racks is very high and picks up a very largethermal load from multiple computers, the small additional load fromother sources may be negligible, apart from perhaps a small latent heatload caused by workers, which may be removed by a smaller auxiliary airconditioning unit as described above.

Cooling water may be provided from a cooling water circuit powered bypump 124. The cooling water circuit may be formed as a direct-return, orindirect-return, circuit, and may generally be a closed-loop system.Pump 124 may take any appropriate form, such as a standard centrifugalpump. Heat exchanger 122 may remove heat from the cooling water in thecircuit. Heat exchanger 122 may take any appropriate form, such as aplate-and-frame heat exchanger or a shell-and-tube heat exchanger.

Heat may be passed from the cooling water circuit to a condenser watercircuit that includes heat exchanger 122, pump 120, and cooling tower118. Pump 120 may also take any appropriate form, such as a centrifugalpump. Cooling tower 118 may be, for example, one or more forced drafttowers or induced draft towers. The cooling tower 118 may be considereda free cooling source, because it requires power only for movement ofthe water in the system and in some implementations the powering of afan to cause evaporation; it does not require operation of a compressorin a chiller or similar structure.

The cooling tower 118 may take a variety of forms, including as a hybridcooling tower. Such a tower may combine both the evaporative coolingstructures of a cooling tower with a water-to-water heat exchanger. As aresult, such a tower may be fit in a smaller space and be operated moremodularly than a standard cooling tower with separate heat exchanger. Anadditional advantage may be that hybrid towers may be run dry, asdiscussed above. In addition, hybrid towers may also better avoid thecreation of water plumes that may be viewed negatively by neighbors of afacility.

As shown, the fluid circuits may create an indirect water-sideeconomizer arrangement. This arrangement may be relatively energyefficient, in that the only energy needed to power it is the energy foroperating several pumps and fans. In addition, this system may berelatively inexpensive to implement, because pumps, fans, coolingtowers, and heat exchangers are relatively technologically simplestructures that are widely available in many forms. In addition, becausethe structures are relatively simple, repairs and maintenance may beless expensive and easier to complete. Such repairs may be possiblewithout the need for technicians with highly specialized knowledge.

Alternatively, direct free cooling may be employed, such as byeliminating heat exchanger 122, and routing cooling tower water(condenser water) directly to cooling coils 112 a, 112 b, as shown inFIG. 2. Such an implementation may be more efficient, as it removes oneheat exchanging step. However, such an implementation also causes waterfrom the cooling tower 118 to be introduced into what would otherwise bea closed system. As a result, the system in such an implementation maybe filled with water that may contain bacteria, algae, and atmosphericcontaminants, such as leaves, dirt, bird feathers or excrement, andinsects or other animals that may enter the tank or mold and may also befilled with other contaminants in the water. A hybrid tower, asdiscussed above, may provide similar benefits without the samedetriments.

In order to keep the water in the cooling tower 118 clean, a watertreatment facility or system 205 can treat water that flows into and outof the cooling tower 118. Because the cooling tower 118 is open to theenvironment, the tower is prone to collecting any debris that is in theenvironment or other items that may accumulate and potentially clog thewater transfer system, i.e., the pipes. The water treatment system 205can reduce or eliminate these contaminants.

The complexity of the water treatment system 205 can vary from a verysimple filtration system to a full-scale water treatment system on parwith municipal water purification or sewage treatment facilities. Thesystem can remove physical, chemical or biological contaminants or anycombination thereof. A very simple system may include a filter-basedsystem, which filters out contaminants over a particular size threshold,such as large contaminants, e.g., anything over 1 inch in size, orcontaminants with a much smaller size, e.g., anything over 25 microns insize. Another simple system can include settling tanks, which allowcontaminants to settle out of the water. A flocculation tank can beused, which aggregates smaller particles into larger particles, whichthen can be more easily removed from the water. Septic tanks,sedimentation tanks, fluidized bed reactors, fixed film system orsuspended growth systems, activated sludge systems, aeration tanks,biofilters or aerobic treatment systems can also be included in thewaste treatment system. Cooling water can be treated by ionization, UVtreatment, reverse osmosis, or chemicals, such as biocides or ozone, toform highly clean water which will then reduce the need for maintenanceon the system because growth of organisms can be prevented in the supercleaned water. The water treatment apparatus can include any combinationof these components or methods of treatment, in addition to a singlemethod by itself.

Determining how to configure the waste treatment system can includedetermining the desired purity level of the treated water, determiningthe acceptable contaminant size of the treated water, as well as thelikely contaminant size of the incoming water and an amount of space,e.g., square footage or acreage, available or required to house thewater treatment system. Additionally, the cost of treatment can be afactor. The cost of purifying the water to potable quality can besufficiently high that it may not be economically feasible (or may bemore expensive than the cost of repairing or replacing piping in thefacility caused by contaminants), particularly because it will becomedirty from exposure to the atmosphere once again. On the other hand, thecost of maintenance can be reduced if the water is sufficiently cleanedto prevent the system from becoming damaged by contaminants. A suitabletype of water treatment apparatus can be determined based on the desireto expend resources on maintaining the system versus the cost oftreating the water using the selected apparatus. In some embodiments,the water is only partially treated and is pumped back into the systemalong with a source of cleaner water. This water is referred to hereinas brown water, not because it necessarily has been used in householdapplications, but because it has already been used in the coolingsystem. Inputting brown water, after only partial treatment, can be usedto reduce the need for clean water from a municipal source.

In addition or as an alternative to adding a water treatment system 205,a filter may be placed in line (not shown) between the cooling tower 118and the data center 101, such as on an outlet of the cooling tower 118.This filter can prevent large contaminants from entering the pipes thatdirect water from the cooling tower 118 to the data center 101. Thefilter can be a single filter or a series of filters for capturingcontaminants and particulates.

The water in the cooling tower 118 can be flowed to the treatment system205 continuously or at regular intervals, so that the cooling tower 118remains at least partially full at any time during operation of the datacenter 101. Because the cooling tower 118 can accumulate sediment orsludge on the interior sidewalls, the entire tower 118 may beperiodically emptied to clean the walls, such as by scrubbing out theinterior of the tower. The location of the cooling tower and seasons maydictate how frequently the tower requires cleaning. For example,bacteria or algae may be more active in warmer months than in coolermonths and therefore more frequent cleaning or treatment may be requiredduring the summer months.

In some embodiments, a portion of the water and contaminants are removedfrom the waste treatment system 205 and instead of being returned to thecooling tower 118, are released as waste, such as to a county ormunicipal sewer system. The percentage that is released as waste candepend on the acceptable limits set by the county or municipalityregarding how concentrated an effluent waste stream from a facility canbe. For example, the waste that is released from the waste treatmentsystem 205 may be a combination of sludge and liquid. Release of somepercentage of waste from the water system allows for flushing mineralsout of the system that might otherwise build up over time andpotentially damage the system.

The waste treatment system 205 is not a part of a governmental waterpollution control facility. Specifically, the waste treatment system 205is a part of the system 100, rather than a separate facility. The wastetreatment system 205 may be physically proximate to the data center 101,such as on a common piece of property, that is, property that is allpart of a single tract, is commonly owned, is within a defined space,such as within a tract of land suitably sized for an industrial use,such as 50 acres, or is commonly fenced in. Because the waste treatmentsystem 205 is near the data center 101 and the cooling system (e.g., onthe same site or an adjacent site), water can be returned from the wastetreatment system 205 directly to the cooling system.

In addition to returning water to the cooling system, such as thecooling tower 118, from the waste treatment system 205, a source offresh water can also be introduced into the cooling tower. Control valve126 is provided in the condenser water circuit to supply make-up waterto the circuit. Make-up water may generally be needed because coolingtower 118 operates by evaporating large amounts of water from thecircuit. The control valve 126 may be tied to a water level sensor incooling tower 118, or to a basin shared by multiple cooling towers. Whenthe water falls below a predetermined level, control valve 126 may becaused to open and supply additional makeup water to the circuit. Aback-flow preventer (BFP) may also be provided in the make-up water lineto prevent flow of water back from cooling tower 118 to a main watersystem, which may cause contamination of such a water system.

In some embodiments, a 30-40 MW facility has a peak flow of about 10,000gallons/minute and uses up to about 15 million gallons per day, e.g., 10million gallons, for cooling. Approximately 5-10% of the water flowingthrough the system can be lost to evaporation, depending on thedimensions of the cooling tower and the ambient conditions. For example,a narrow and deep cooling tower can reduce loss of water in the coolingtower, such as to entrainment in the air stream over the cooling tower.

Approximately 1% of the flow through the data center can be directed tothe waste treatment system 205. Some amount of the flow into the wastetreatment system will be released off-site, such as to the sewer, whilethe remainder is returned to the cooling tower. The amount of water thatis treated from each cycle of water through the cooling system can varydepending on the efficiency of the water treatment system, the tolerancefor contaminants in the cooling system and acceptable cost of treatment.Achieving a higher cleanliness of treated water comes at higher capitalcost, but reduces water consumption by reducing the amount of make upwater needed by the cooling system. In some embodiments, a largerpercentage of water is removed from the system for on-site treatment,such as 10%, each day. A percentage of the treated water, the wastepercentage, can then be sent off-site for disposal or further treatment.The more water that is removed from the system for cleaning each day,the lower the level of water cleanliness coming out of the wastetreatment system back to the cooling tower needs to be to achievesufficiently clean water that is acceptable for the desired maintenanceschedule.

A portion of the treated water is returned to the cooling tower forreuse. Because the water is used for cooling and not for humanconsumption, the quality of the treated water may not be that of watersourced from a potable drinking source, but can be sufficiently clean toprevent damage to the cooling system. Because there will be some loss ofwater either to evaporation or as waste that is sent off-site, themake-up water is used to ensure that there is sufficient water in thesystem to keep the data center sufficiently cooled or that there issufficient water to keep the total amount of water in the systemconstant. The make-up water can be provided by a main water system,e.g., a municipal water system, or from another source, such as capturedprecipitation, surface water or ground water. In some systems, thesource of make-up water is effluent from an industrial or agriculturalplant that either is sufficiently clean for delivering to the system orwhich can be cleaned by the waste treatment system for delivering to thesystem. Because many plants are required to have their own treatmentcenters on-site, the water coming out of these plants may be cleanenough to use with the cooling system. Further, diverting this effluentto the data center cooling system can allow the plant to save on sewercosts.

Referring back to FIG. 1, optionally, a separate chiller circuit may beprovided. Operation of system 100 may switch partially or entirely tothis circuit during times of extreme atmospheric ambient (i.e., hot andhumid) conditions or times of high heat load in the data center 101.Controlled mixing valves 134 are provided for electronically switchingto the chiller circuit, or for blending cooling from the chiller circuitwith cooling from the condenser circuit. Pump 128 may supply tower waterto chiller 130, and pump 132 may supply chilled water, or cooling water,from chiller 130 to the remainder of system 100. Chiller 130 may takeany appropriate form, such as a centrifugal, reciprocating, or screwchiller, or an absorption chiller.

The chiller circuit may be controlled to provide various appropriatetemperatures for cooling water. In some implementations, the chilledwater may be supplied exclusively to a cooling coil, while in others,the chilled water may be mixed, or blended, with water from heatexchanger 122, with common return water from a cooling coil to bothstructures. The chilled water may be supplied from chiller 130 attemperatures elevated from typical chilled water temperatures. Forexample, the chilled water may be supplied at temperatures of 55° F.(13° C.) to 65 to 70° F. (18 to 21° C.) or higher. The water may then bereturned at temperatures like those discussed below, such as 59 to 176°F. (15 to 80° C.). In this approach that uses sources in addition to, oras an alternative to, free cooling, increases in the supply temperatureof the chilled water can also result in substantial efficiencyimprovements for the system 100.

Pumps 120, 124, 128, 132, may be provided with variable speed drives.Such drives may be electronically controlled by a central control systemto change the amount of water pumped by each pump in response tochanging set points or changing conditions in the system 100. Forexample, pump 124 may be controlled to maintain a particular temperaturein workspace 106, such as in response to signals from a thermostat orother sensor in workspace 106.

In operation, system 100 may respond to signals from various sensorsplaced in the system 100. The sensors may include, for example,thermostats, humidistats, flowmeters, and other similar sensors. In oneimplementation, one or more thermostats may be provided in warm airplenums 104 a, 104 b, and one or more thermostats may be placed inworkspace 106. In addition, air pressure sensors may be located inworkspace 106, and in warm air plenums 104 a, 104 b. The thermostats maybe used to control the speed of associated pumps, so that if temperaturebegins to rise, the pumps turn faster to provide additional coolingwaters. Thermostats may also be used to control the speed of variousitems such as fan 110 to maintain a set pressure differential betweentwo spaces, such as attic 105 and workspace 106, and to thereby maintaina consistent airflow rate. Where mechanisms for increasing cooling, suchas speeding the operation of pumps, are no longer capable of keeping upwith increasing loads, a control system may activate chiller 130 andassociated pumps 128, 132, and may modulate control valves 134accordingly to provide additional cooling.

Various values for temperature of the fluids in system 100 may be usedin the operation of system 100. In one exemplary implementation, thetemperature setpoint in warm air plenums 104 a, 104 b may be selected tobe at or near a maximum exit temperature for trays in racks 102 a, 102b. This maximum temperature may be selected, for example, to be a knownfailure temperature or a maximum specified operating temperature forcomponents in the trays, or may be a specified amount below such a knownfailure or specified operating temperature. In certain implementations,a temperature of 45° C. may be selected. In other implementations,temperatures of 25° C. to 125° C. may be selected. Higher temperaturesmay be particularly appropriate where alternative materials are used inthe components of the computers in the data center, such as hightemperature gate oxides and the like.

In one implementation, supply temperatures for cooling water may be 68°F. (20° C.), while return temperatures may be 104° F. (40° C.). In otherimplementations, temperatures of 50° F. to 84.20° F. or 104° F. (10° C.to 29° C. or 40° C.) may be selected for supply water, and 59° F. to176° F. (15° C. to 80° C.) for return water. Chilled water temperaturesmay be produced at much lower levels according to the specifications forthe particular selected chiller. Cooling tower water supply temperaturesmay be generally slightly above the wet bulb temperature under ambientatmospheric conditions, while cooling tower return water temperatureswill depend on the operation of the system 100.

Using these parameters and the parameters discussed above for enteringand exiting air, relatively narrow approach temperatures may be achievedwith the system 100. The approach temperature, in this example, is thedifference in temperature between the air leaving a coil and the waterentering a coil. The approach temperature will always be positivebecause the water entering the coil is the coldest water, and will startwarming up as it travels through the coil. As a result, the water may beappreciably warmer by the time it exits the coil, and as a result, airpassing through the coil near the water's exit point will be warmer thanair passing through the coil at the water's entrance point. Because eventhe most-cooled exiting air, at the cooling water's entrance point, willbe warmer than the entering water, the overall exiting air temperaturewill need to be at least somewhat warmer than the entering cooling watertemperature.

Keeping the approach temperature small permits a system to be run onfree, or evaporative, cooling for a larger portion of the year andreduces the size of a needed chiller, if any is needed at all. To lowerthe approach temperature, the cooling coils may be designed forcounterflow rather than for self-draining. In counter-flow, the warmestair flows near the warmest water and the coolest air exits near wherethe coolest water enters.

In certain implementations, the entering water temperature may be 64° F.(18° C.) and the exiting air temperature 76.6° F. (24.8° C.), as notedabove, for an approach temperature of 12.6° F. (10.8° C.). In otherimplementations, wider or narrower approach temperature may be selectedbased on economic considerations for an overall facility.

With a close approach temperature, the temperature of the cooled airexiting the coil will closely track the temperature of the cooling waterentering the coil. As a result, the air temperature can be maintained,generally regardless of load, by maintaining a constant watertemperature. In an evaporative cooling mode, a constant watertemperature may be maintained as the wet bulb temperature stays constant(or changes very slowly), and by blending warmer return water withsupply water as the wet bulb temperature falls. As such, active controlof the cooling air temperature can be avoided in certain situations, andcontrol may occur simply on the cooling water return and supplytemperatures. The air temperature may also be used as a check on thewater temperature, where the water temperature is the relevant controlparameter.

FIG. 3A is a psychrometric chart showing a heating and cooling cycle forair in a data center. A psychrometric chart graphically represents thethermodynamic properties of moist air (which is air containing anyappreciable moisture, and not merely air that would feel moist to aperson). The chart is from ASHRAE Psychrometric Chart No. 1, whichdefines properties of air for sea level applications. See 1997 ASHRAEHandbook—Fundamentals, at page 6.15. Other charts may also be used, andthe chart shown here is merely used to exemplify certain aspects of theconcepts discussed in the present document.

The psychrometric chart is criss-crossed with a number of lines thatrepresent various properties of air. Cooling and heating processes onair can be analyzed by identifying a point on the chart that representsair at a particular condition (e.g., temperature and humidity), and thenlocating another point that represents the air at another condition. Aline between those points, generally drawn as a straight line, may befairly assumed to represent the conditions of the air as it moves fromthe first condition to the second, such as by a cooling process.

Several properties will be discussed here. First, saturation temperatureis an arc along the left of the graph and represents the temperature atwhich air becomes saturated and moisture begins coming out of the air asa liquid—also known popularly as the “dew point.” When the temperatureof air is taken below the dew point, more and more water comes out ofthe air because the cooler air is capable of holding less water.

The dry bulb temperature of air is listed along the bottom of the graphand represents what is popularly viewed as temperature, i.e., thetemperature returned by a typical mercury thermometer.

The chart shows two numbers relating to the humidity of air. The firstis the humidity ratio, listed along the right edge of the graph, and issimply the weight of moisture per each unit weight of dry air. Thus, thehumidity ratio will stay constant at various temperatures of air, untilmoisture is removed from the air, such as by pushing the air temperaturedown to its dew point (e.g., the moisture comes out of the air and endsup on the grass in the morning) or by putting moisture into the air(e.g., by atomizing water into such as fine mist in a humidifier thatthe mist can be supported by the natural motion of the air molecules).Thus, when graphing processes that involve simple changes in airtemperature, the point that represents the state of the air will movestraight left and right along the graph at a constant humidity ratio.That is because the dry-bulb temperature will go up and down, but thehumidity ratio will stay constant.

The second humidity parameter is the so-called relative humidity. Unlikethe humidity ratio, which measures the absolute amount of moisture inthe air, the relative humidity measures the amount of moisture in theair as a percent of the total moisture the air could possibly hold atits current temperature. Warmer air can hold more moisture than cancolder air, because the molecules in warmer air are moving more rapidly.Thus, for an equal amount of moisture in the air (i.e., an equalhumidity ratio), the relative humidity will be lower at a hightemperature than at a low temperature.

As one example, on a summer day when the overnight low was 55 degreesFahrenheit and there is dew on the ground, and the daytime high isaround 75 degrees Fahrenheit, the relative humidity in the early morningwill be about 100% (the dew point), but the relative humidity in theafternoon will be a very comfortable 50%, even if one assumes that theidentical amount of water is in the air at both times. This exemplaryprocess is shown in FIG. 3 by the points marked C and D, with point Cshowing saturated air at 55 degrees Fahrenheit (the overnight low), andpoint D representing that same air warmed to 75 degrees Fahrenheit (thedaytime temperature).

Commercial air handling systems take advantage of this same process inproviding conditioned air in a building. Specifically, systems maygather air from an office space at 75 degrees Fahrenheit and a relativehumidity of 60 percent. The systems pass the air through a cooling coilthat looks like an automobile radiator to cool the air to 55 degreesFahrenheit, which will typically push the air down to its dew point.This will make moisture pour out of the air as it passes through thecooling coil. The moisture can be captured in drains below the coolingcoil and then be removed from the building. The air can then be returnedto the work space, and when it warms back to 75 degrees, it will be avery comfortable 50 percent relative humidity.

This common cooling process is shown by points A, B, C, and D on thechart of FIG. 3A. Point A shows the 75 degree air at 70 percent relativehumidity. Point B shows the air cooled to its dew point, which it hitsat a temperature (dry bulb) of about 65 degree Fahrenheit. Furthercooling of the air to 55 degrees Fahrenheit (to point C) rides along thesaturation curve, and water will come out of the air during that portionof the cooling. Finally, the state of the air moves to point D as theair is warmed and reaches 75 degrees Fahrenheit again. At this point,the relative humidity will be 50 percent (assuming it does not pick upadditional moisture from the room or the existing room air) rather thanthe original 60 percent because the cooling process has dehumidified theair by pulling moisture out of the air in the cooling coil. If the roomair contains more moisture than does the cooled air, point D will beslightly above its position shown in FIG. 2, but still below point A.

Such a common process brings with it a number of challenges. First, tocool the air to 55 degrees Fahrenheit, the system must provide coolingwater in the cooling coil that can absorb all the heat. Such water wouldneed to be at least cooler than 55 degrees Fahrenheit. It may beexpensive to create such cool water—requiring systems such as chillersand other energy-intensive systems. In addition, the area immediatelyaround the pipes that supply the cooling water will be cooler than 55degrees Fahrenheit, i.e., cooler than the dew point of the air if thepipes run through the workspace or through air having the same state asthe air in the workspace. As a result, moisture from the air maycondense on the pipe because the temperature of the surrounding air hasfallen to its dew point. Thus, insulation may be required around thecool pipes to prevent such condensation, and condensation might occur inany event, and cause rusting, mold, water pooling, or other problems.Finally, as any high school physics student likely knows, it takes a lotof energy to dehumidify, i.e., to change the water from one state toanother.

The warm air cooling features discussed with respect to FIG. 1 abovemay, in certain implementations, avoid one or more of these challenges.An exemplary warm air cooling process is shown on the graph of FIG. 2 bypoints E and F. Point E shows a room-air condition in a workspace thatis near the top of, but within, common guidelines for comfort levels forpeople dressed in summer clothing. See 1997 ASHRAEHandbook—Fundamentals, at page 8.12. That condition is 75° F. (24° C.),and a relative humidity of about 70 percent (the same as Point A in theprior example). Point F shows heating of that air without the additionof moisture, such as by passing the air over heat-generating computercomponents in a rack-mounted server system. The temperature rise is 36°F. (2° C.) to bring the air to a state of 111° F. (44° C.) at about 23percent relative humidity. The air may then be cooled to its originaltemperature (point E) of 75 degrees Fahrenheit in a cooling coil beforeit is re-introduced to the work space, without adding water to orremoving water from the air.

Points G and H on the graph represent the condition of air in the spaceimmediately surrounding cooling pipes. It is assumed for this examplethat the cooling supply water is 68 degrees Fahrenheit (20 degreesCelsius) and the return temperature is 104 degrees Fahrenheit (40degrees Celsius). It is also assumed that the air near the pipes willcontain the same moisture level as the rest of the air in the space, andthat the air immediately surrounding the pipe takes on the sametemperature as the water inside the pipe. As can be seen, this airassociate with the cooling water also stays above the saturation point,so that there should be no condensation on the cooling water pipes, andthus no need for insulation to prevent condensation on the pipes.

It can be seen by this process that the air never becomes saturated. Asa result, the system need not provide energy to create a phase change inthe air. In addition, the system need not provide liquid recoverystructures at the cooling coil, or pipe insulation for anywhere. Othersimilar temperatures, and in many implementations warmer temperatures,may be used. The particular temperatures discussed here are meant to beexemplary only.

FIG. 3B is a graph of setpoint temperature for a computing facility overa one year time period. The setpoint temperature may be a temperature ina work space such as work space 106 in FIG. 1. An example outdoorwetbulb temperature through the year is also shown for comparison. Asshown in the stepped graph, the setpoint temperature (i.e., a targetedtemperature) is adjusted infrequently, such as with the seasons ormonthly, so as to more closely track expected outdoor temperatures. Thesetpoint is increased in the summer because the lower winter setpointmay be effectively unattainable in warm summer weather by using onlyevaporative cooling. Thus, while a “best,” lower, setpoint temperatureapplies in the winter, that same setpoint is not realistic, in theexample, in summer months.

The setpoint is adjusted infrequently so as to better approximate asetpoint that is attainable using evaporative cooling techniques withlittle or no assistance from chillers or other similar components thatrequire relatively high levels of energy to operate. Although increasingthe setpoint during warmer times of the year may increase the typicaloperating temperature, it also decreases the amount of thermal cyclingthat may occur in a facility, and thus lengthen the life of electroniccomponents in the facility. In contrast, if the setpoint is kept as lowas possible, the conditioned space would be relative cool on days havinga low wet bulb temperature and relatively warm on days having a high wetbulb temperature. Thus, keeping a constant setpoint throughout the yearmay actually increase thermal cycling, particularly in warmer months—asthe system is able to maintain the setpoint on some days but not onother days.

The setpoint may also be adjusted substantially continuously, such as byvarying the setpoint temperature in an annual sinusoidal manner thatgenerally follows the expected outdoor wet bulb temperature, as shown bythe continuous setpoint line. Studies have indicated that humandiscomfort is minimized by providing many minute changes, or continuouschanges, to temperature, as opposed to large step variations intemperature. In both examples the setpoint may be maintained, in certainimplementations, even if a lower temperature may readily be achieved(e.g., because the outdoor wet bulb temperature is lower than expected)so as to minimize thermal cycling in a facility being cooled.

The particular setpoint temperatures may be selected based on thecapabilities of the components in a facility and on prevailing localweather conditions. For example, cool weather setpoints may be in therange of 59-77° F. (15-25° C.), with particular values of 64.4, 68,71.6, and 75.2° F. (18, 20, 22, and 24° C.). Warm weather setpoints maybe in the range of 68-86° F. (20-30° C.), with particular values of71.6, 75.2, 78.8, and 82.4° F. (22, 24, 26, ad 28° C.). In a particularimplementation, warm weather air temperatures in a facility may beapproximately 80.60-82.40° F. (27-28° C.) and cold weather temperaturemay be about 71.60° F. (22° C.). The time for resetting the setpoint mayalso vary, and may be weekly (e.g., using a long range weather forecastto select an achievable setpoint that tracks the predicted wet bulbtemperature), weekly, monthly, or quarterly, for example.

When the wet bulb temperature gets too high to achieve the desired setpoint, the temperature of the cooling water may be allowed to driftupward with the wet bulb temperature, causing the temperature in space106 to move upward also. Alternatively, cooling such as from chiller 130may be provided, and the chilled water may be blended with other coolingwater so that the setpoint may be maintained.

Cooling with relatively warm water may also provide certain benefitswhen chillers are used. In particular, when a chiller is allowed toprovide a smaller temperature change to a coolant, it may providecooling for less electrical consumption per ton of cooling than if itwere required to impart a greater temperature change to the coolant. Byhaving elevated air temperatures in a cooled space, the supply watertemperature may likewise be higher, and the need for a chiller to coolthe water may be less.

FIG. 4 is a plan view in schematic form of a hydronic cooling system fora data center 300. The data center 300 includes an existing plant 302,and a future plant 304. As will be seen, the system is highly modular,and can therefore be scaled from a very small system to a very largesystem by adding additional components and subsystems. Although theexisting and future systems are shown as separate systems, extensions ofthe existing system may also be employed for future expansion. Forexample, oversized piping may be installed in some implementations andmay be tapped for future additions of added components when the datacenter 300 is expanded. Also, other forms of cooling loops, oradditional or alternative cooling loops may be employed.

The cooling system for existing plant 302 is similar to that shown inFIG. 1. Cold air is supplied to a workspace 306 by air handling unit310. Air handling unit 310 may include a supply fan (not shown) thatdraws warm air out of a plenum, such as in an above-ceiling attic space,and pushes the air through cooling coils 312, 314. The warm air may beproduced by passing cooled air over computers, such as computer, mountedon trays in a rack system. Air passing over the computers may becollected in warm-air plenums 316, and may be routed to theabove-ceiling space or another appropriate space.

In alternative implementations, multiple air handling units that includea fan and a cooling coil may be placed immediately above or below thewarm air plenums 316. Such air handling units may take the form of longbanks of small centrifugal fans and long heat exchange units mounted tothe fans. The fans may pull air or push air through the coils. Pushingair may have the advantage of being quieter, as the coils may block outa certain amount of the fan noise. Also pushing of air may be moreefficient. Pulling of air may provide a benefit of allowing a limitednumber of fans to operate on a much larger bank of coils, as all thepulling fans can be connected to a plenum, and may create a relativevacuum behind the coils to pull air through. In such an arrangement, ifone of the fans breaks down, the others can more easily provide supportacross the entire coil length.

Cooling water may be provided by pumps 326 to cooling coils 312, 314 tocool the air. These pumps 326 may draw cooled water from heat exchangers324, and drive the water into existing plant 302, through cooling coils312, 314, and back through heat exchangers 324, where the heat acquiredfrom coils 312, 314, may be removed from the water.

Heat in the cooling water may be removed from heat exchangers 324 bycooled tower water supplied through pump 322 from cooling towers 320.The system is shown for exemplary purposes as having two parallelcircuits for cooling water and one circuit for tower water from thecooling towers 320. However other appropriate arrangements for thepiping system may also be used. For example, a single heat exchanger maybe used, as may a single cooling tower. Other sources of free coolingmay also be used, such as ground water or deep lake cooling.

Also, additional space may be provided for extra cooling towers andfuture heat exchangers, and piping may be sized to accommodate futureexpansion. For example, cooling towers may be provided in an extendablestacked arrangement, so that a third tower will be piped in parallelwith the first two towers 320 when the additional cooling is needed.

Existing plant 302 includes an additional workspace 308. This space maybe for example, an office space, control room, or storage room. Thespace may be designed to be inhabited extensively by people, and mayrequire lower temperatures than does workspace 306. As a result,workspace 308 is provided with air-conditioning unit 330, which may be astandard rooftop air conditioning unit. Although air-conditioning unit330 may require additional electricity for providing higher degrees ofcooling, including latent heat removal, the unit 330 generally serves anarea and a thermal load that is much smaller than the entire system. Asa result, unit 330 may be much smaller than what would otherwise berequired to provide similar low-temperature cooling for the rest of thesystem.

Although not shown, one or more chillers and chillers circuits may beprovided to operate the system, in addition to the tower cooling watercircuit, whether together or alternatively. The piping of the chillercircuit may take a form similar to that shown schematically in FIG. 1.

As noted above, future plant 304 may be provided in a variety of ways.In general, a modular approach may be used, so that additional heatexchangers are added in a size commensurate with the additional loadsthat are expected. Certain components may be piped as entirely separatecircuits, while others may be extensions of the original system. Sharingcomponents between old and new systems may cause construction-basedinterruptions in the existing system, but may also provide for betterutilization of the components in the full system. For example, condenserwater can be shared through the system, so that if each half of thesystem requires cooling from 1.5 cooling towers, only three towers willbe operated. If the two systems are separate, each system would have torun two towers, and thereby use additional energy.

FIG. 5 is a plan view in schematic form of a hydronic cooling system fora data center housed in outdoor shipping containers 402 and 404. Thesystem is arranged in a manner similar to the system in FIG. 4. Here,however, cooling coils are mounted along the length of both of shippingcontainers 402, 404, such as below or above the computer-holding racksin the system. For example, an elevated false floor may be provided downthe center of the shipping containers 402, 404, and squirrel cage orother forms of fans may blow or pull warm air through cooling coils,depositing cool air into the space under the grate. The cooled air maythen pass up through the floor grate into cooled-air isles 400, 403, andthen drawn by fans associated with each tray in the racks, into warm-airplenums 401, 405 along the sides of the shipping containers, and may berouted back through the fans. Using exterior space along the outer wallsfor the warm-air plenums 401, 405 may have the advantage of allowingdirect rejection of heat on cold days and of minimizing the amount ofatmospheric heat that passes into each container on hot days.

In this implementation, the various benefits of using little energy, ofmodularity, and of standardization on low complexity components may beappreciated. Specifically, shipping containers 402, 404 may be built andoutfitted in a central location using standardized techniques andspecialized, well-trained labor—a type of prefab construction approach.The shipping containers 402, 404 may then be delivered to a site, suchas a site having adequate electrical, water, and data services, and maybe easily connected to such services, and then begin their operation.

The other components of the system may be provided separately to thesite. For example heat exchangers and pumps may be provided onpreassembled skids, dropped into the place, and connected to othercomponents. Cooling towers may also be delivered to a site and connectedrelatively quickly. Also, because the system may operate without theneed for components such as chillers that demand high power levels, thesystem may be installed in more areas, such as remote areas having lowerlevels of electrical service.

As shown, the system is also highly modular, so that additionalresources may be added relatively quickly and inexpensively as they areneeded. Containers 402 are shown as part of an existing system, andcontainers 404 (with associated equipment) are shown as part of a futureaddition to the system. Other modules may also be added as the needarises, until the level of available utilities is tapped out. Eachcontainer may contain hundreds or thousands of trays, so that a completeinstallation could include hundreds of thousands of computers.

Systems like those shown in this document may be deployed in a number ofdifferent and flexible manners. For example, locations may be selectedaccording to the availability of resources. For example, cooling watermay be obtained from ground water or surface water for free coolingprocesses. In such an environment, cooling towers may be eliminated fromthe system.

In addition, systems may be deployed far from suitable constructionlabor (and may use labor having a lower skill level) if they areassembled centrally and shipped to a site.

Such systems may also be self-contained. For example, fuel cells orgas-powered turbines may be deployed with a system to generateelectricity, and may be supplemented by wind or solar power. Inaddition, generators, such as combustion turbines may be selected forless than the full load of a system, but may be deployed to permitpeak-shaving of the power required by a system. Such peak-shaving maypermit a system to operate in an area that cannot provide all of thepower needed for a system. In addition, peak shaving may allow anoperator of the system to negotiate energy rates that are lower thanwould otherwise be available, because the system would not be drawinghigh levels off the grid when the electrical provider does not have suchextra capacity. Moreover, heat from the turbines may be used to helppower equipment such as an ammonia-based absorption chiller. Inaddition, Peltier-like devices may be used to convert heat intoelectrical energy. In addition, excess pressure from make-up waterapplied to the cooling towers may also be used to drive small turbinesfor limited electrical production.

Such systems may also be co-located with other systems that may have usefor the hot water generated through the cooling of electroniccomponents. For example, a data center may be located near a hospital orother high density residence to supply heating water, such as for spaceheating or water heating. In addition, the hot water may be used incommon with various processes, such as fermentation, manure digestion,yogurt culture fabrication, and ethanol production. Moreover, the hotwater may be used to heat swimming pools or other buildings, or may berun through ice and snow melt piping, such as in airport runways.Likewise, heat from the system may be used to control temperatures in aco-located fish farm. Other implementations may also be employed toserve particular needs for data services, particularly wheredistribution of processing power closer to end users is needed.

FIG. 6 is a flowchart 600 showing steps for cooling a data center usingelevated temperatures. The method is exemplary only; other steps may beadded, steps may be removed, and the steps may be performed in differentorders than those shown, as appropriate.

At box 602, the exhaust temperatures of various trays in a computer racksystem are maintained at a computed value, such as a maximum value formaintaining the trays in reliable operation. The trays may each beself-throttling, in that a fan and related temperature sensor may beassociated with each tray. At box 604, at the same time other componentsof the system may maintain a workspace temperature in front of the racksat a particular temperature, such as a maximum allowed temperature. Themaximum allowed temperature may be, for example, a maximum temperatureat which the workers in the workspace are willing to operate. It mayalso be a temperature set by law or regulation, such as a maximum 40degree Celsius limit. Federal OSHA and California OSHA guidelines mayprovide limitations on such temperatures. The set temperature may alsochange at appropriate times; for example, the temperature may be higherduring times when people are not expected to be in the workspace.

At box 606, the workspace cooling is changed in response to changes inthe system. Such changes may occur, for example, if the set temperaturefor the space changes. The changes may also occur, for example, if thetemperature remains constant but the load on the system changes—such asif an additional rack of computers is powered up, or if the computersare loaded more heavily. The cooling may change, for example, byincreasing the rate of pumping cooling fluid through cooling coils.Alternatively, additional coils may be brought on-line, or a chiller maybe started to lower the temperature of cooling water.

At box 608, the exhaust temperature of air from the computer racks ismaintained at the maximum computer value. Specifically, although theworkspace temperature has changed, and other parameters in the systemmay have changed, the exhaust temperature may remain unaffected, as eachfan associated with a tray remains set on one exhaust temperature.

FIG. 7A shows an alternative embodiment of a cooling system 705 from thesystem shown in FIG. 1. In addition to a cooling tower 118, the coolingsystem 705 includes a primary storage tank 710. Water that has beenreduced in temperature in the cooling tower 118 is routed to the primarystorage tank 710. In some embodiments, the water from the primary waterstorage tank 710 flows directly from the primary water storage tank 710to a heat exchanger 122. However, if the water from the primary waterstorage tank 710 is not sufficiently cool, cooler water can be mixedwith the water from the primary water storage tank 710 to bring thetemperature down.

In some embodiments, water from the primary storage tank 710 is firstrouted to a secondary storage unit. The secondary storage unit includeseither a single tank or two tanks. Secondary storage units that includetwo tanks have a buffering tank 720 and a thermal storage tank 722. Thebuffering tank 720 and thermal storage tank 722 can isolate water withintheir tanks or may be connected to one another, such as by a series ofbaffles that allow some water to flow between the two tanks. Water fromthe primary storage tank 710 flows into, and in some cases, back out ofthe secondary storage buffering tank 720 to supply the buffering tank720 with water.

In order to provide cooler water than is available from the primarystorage tank 710 for feeding the heat exchanger 122, water from thesecondary storage unit is circulated through the evaporator or cold sideof the chiller 130. The chiller lowers the temperature of the water inthe secondary storage unit to a temperature that is suitable for mixingwith water from the primary storage tank 710 for delivery to the heatexchanger 722. If the secondary storage unit includes two compartments,the water can be directed from the buffering tank 720 to the chiller130, and the thermal storage tank 722 can retain chilled water from thechiller 130 until needed. One advantage of storing chilled water is inthe event that the chiller 130 goes off-line and needs to be restarted,a sufficient supply of water can be stored, which allows the coolingsystem 705 to continue to operate until the chiller 130 is back inservice. In some embodiments, a suitable size of a thermal storage tank722 for each 2 MW of data center power use is about 4000 gallons. Asuitable buffering tank 720 size can be about 11,000 gallons.

The condenser side, or hot side, of the chiller 130 can be fed by waterfrom the primary storage tank 710. The chiller then pumps heat from thewater taken from the secondary storage unit into water from the primarystorage tank 710. The warmed water is then routed to the cooling tower118 for cooling.

In some embodiments, the primary storage tank 710 holds about the samequantity of water as a small residential swimming pool, such as about15,000 gallons, which can be suitable for each 2 MW of data center load.At any size, when the temperature drops at night, the water temperaturein the primary storage tank 710 and the cooling tower 118 drops as well.This temperature can be sufficiently low for proper operation of theheat exchanger 122 and components (e.g., the coils) in the data centerfor removing heat from the electronic devices. Thus, the day/nighttemperature differential can be taken advantage of to reduce use of thechiller 130. The water chilled at night in the primary storage tank 710can also be transferred to the secondary storage unit for use later inthe day when the water temperatures begin to climb. As temperaturesclimb outside and the temperature in the water from the cooling towerrises, this water is mixed with the stored cooler water from the primaryand/or secondary storage tanks so that the water entering the heatexchanger remains in the proper temperature range. This can result inthe temperature of the water entering the heat exchanger varying over a24-hour cycle, being somewhat cooler at night and warming during theday.

The water temperature can also fall so low as to be too cold to feeddirectly to the heat exchanger 122. As noted herein, water that is toocold can cause condensation if the temperature of the componentscarrying the chilled water is below that of the dew point. To avoidcondensation and the need for expensive insulation, the water throughcooling system 705 is kept above a threshold temperature. Thus, it isnot desirable to feed water to the heat exchanger 122 that is below thatthreshold temperature. When the temperature of the water in the primarystorage tank 710 is too low, warmed water from the heat exchanger can befed directly into the primary storage tank 710 (bypassing the coolingtower) to increase the temperature to within the desirable range. Thus,the primary tank acts as a mixer. Alternatively, heated water from theheat exchanger 122 can be mixed with water coming from the primarystorage tank 710 and being fed to the heat exchanger 122 (route notshown).

Transferring chilled water from the primary storage tank 710 to thesecondary storage unit can provide a source of chilled water without theuse of the chiller. As the water in the primary storage tank 710 warmsup, chilled water can be drawn directly from the secondary storage unitto reduce the temperature of water supplied to the heat exchanger 122.Thus, variations in ambient temperature, such as day/night variations orday-to-day variations, can be taken advantage of to reduce chiller user.

In some embodiments, multiple primary storage tanks 710 are used with asingle data center. With a sufficient number of primary storage tanks710, a half day or day-long outage of water can be covered by the waterin the primary storage tanks. Greater quantities of water can allow forlonger outages of water or for shaving off the effects of peaktemperatures experienced in the environment over a time greater than aday. However, such quantities of water can be impractical to keepon-site. Under normal operating conditions, the primary storage tanks710 can be kept full. If a make-up source of water is not available forsome period, the primary storage tanks may be allowed to drain to somefraction of their capacity, such as 20% of capacity, until make-up wateris again available.

In order to regulate the flow of water to the heat exchanger, whetherchilled water is introduced into the flow path, the operation of thechiller and the general flow of water through the cooling system 705, acontroller 730 can be included in the cooling system 705. The controller730 can control valves 134 along each of the water lines as well asoperation of the chiller 130 and heat exchanger 122. Optionally, thecontroller can also provide a warning for data control center that thereis a problem with one of the components in the system. The controllercan either include or be in communication with sensors that indicate theambient temperature and the optimal operating conditions for the system.

As shown in FIG. 7B, the controller can determine the routing of thewater through the cooling system according to method 740. Thetemperature of the water in the primary storage tank can be measured orobtained by the controller (step 742). If the temperature of the waterin the primary storage tank is within a suitable range for routing tothe heat exchanger, then the water from the primary storage tank isrouted directly to the heat exchanger (step 744). If, however, the wateris below a suitable range for delivering to the heat exchanger directly,water coming out of the heat exchanger is first mixed with the waterfrom the primary storage tank (step 746). As noted herein, the mixingcan occur in the primary storage tank or along the piping that leads tothe heat exchanger. The mixed water is then routed to the heat exchanger(step 744).

On the occasions when the water in the primary tank is above the desiredtemperature range, the system then determines whether there is chilledwater stored in the secondary storage tank for mixing with the waterfrom the primary storage tank (step 752). If the water in the secondarytank is sufficiently cool for mixing with the water from the primarytank or if there is a sufficient quantity of chilled water in thesecondary storage tank, then water from both the primary and secondarystorage tanks are flowed through the cooling system (step 760). Themixed water from the primary and secondary storage tanks is then routedto the heat exchanger (step 744). If the water in the secondary storagetank is not suitably cold or of there is not enough chilled water to mixwith the water from the primary storage tank, water can be flowedthrough the chiller to reduce the temperature (step 764). The water thatis chilled by the chiller is then mixed with water from the primarystorage tank (step 768). The mixed water is then routed through the heatexchanger (step 744). These steps are then repeated, such as bycontinuously monitoring the temperature of water flowing through thesystem and being stored in each of the storage tanks, and adjusting flowas required to keep the water entering the heat exchanger at the desiredtemperature.

In some implementations of data centers, water returning from the heatexchanger 122 is routed to a holding tank (not shown) beneath the datacenter. The holding tank can take the place of one of the storage tanksor can be used in addition to the storage tanks. Storing water beneaththe data center can reduce piping needs. Alternatively, water from thecooling tower 118 can be routed to a holding tank beneath the datacenter. Because the water is cooler after cooling off in the coolingtower, there is less likelihood of condensation forming under the datacenter than if water from the heat exchanger is routed to the holdingtank. The holding tank can provide a space efficient means for storingwater, particularly if water outages may be possible, such as atparticular times of the year when surface water may be frozen andinaccessible.

As in other systems, a water treatment system 205 can be coupled to oneor more of the storage tanks or the cooling tower to treat any water andreduce the need for maintenance on the system. Although not shown, thewater treatment system 205 can optionally be fed by a non-potable watersource to reduce the system's use of municipal or county water. Forexample, the system 705 can use water that is not sufficiently clean forhuman consumption and that is from a local source, and treat the waterbefore introducing it to the system 705. Alternatively, a source ofmake-up water can be fed directly to the primary storage tank 710.

Referring to FIG. 8, in addition to a water treatment apparatus, asettling pond 850 can be located proximate to the cooling system or thewater treatment system 205. The settling pond 850 can retain water forsufficiently long periods that any sediment is permitted to settle outof the water. The settling pond 850 can provide for massive thermalstorage. Reduced settlement water from the settling pond can also thenbe routed back to the cooling system. In some embodiments, the water isfirst treated at the water treatment system 205 before entering thewater cooling system. The settling pond 850 can provide further back upwater supply when water is not available from a regularly used source,such as city water.

Either the settling pond 850 or another large tank can provide massivethermal storage for the cooling system. For example, a pond or tank thatis sufficiently large to hold 100,000 gallons can provide a day's worthof thermal mass for tempering the peaks and troughs of temperaturechange for each 2 MW of data center load. For seasonal tempering oftemperature peaks and troughs, millions of gallons of water may berequired for each 2 MW of data center load. Thus, in some embodiments,the settling pond or large storage tank is sized to average out thetemperature change of a season or even a year. That is, massive thermalstorage can be provided for the cooling system by providing a tank orpond that holds millions of gallons of water.

Optionally, a reflective cover can be located over the settling pond850. The reflective cover can keep the water in the settling pond 850from heating up or from evaporating. In some embodiments, the settlingpond 850 has a deep central portion where primary settling occurs and ashallow periphery portion provided for wildlife usage. For example, theshallow periphery can include a reed bed or other similar methodology,which can provide a high degree of aerobic biological improvement to thewater. The water from the deeper central portion can be recycled to thecooling system, while the water in the shallow periphery is leftundisturbed.

Because the data center can be scaled to any size for which sufficientpower to run the center is available, the cooling systems can bemodularized. In some embodiments, cooling systems are built as moduleswith a housing that is small enough to be transported over highways,such as, modules having a width less than 13.5 feet, such as about 12feet, and a length of less than 97 feet, such as less than 30 feet orless than 10 feet. Each module can include one or more of a heatexchanger, a chiller or a controller. Optionally, a module can alsoinclude a primary and second water storage tank and a cooling tower,such as on top of the tanks. Alternatively, as shown in FIG. 9, a modulewith the heat exchanger and controls are connected to a separate systemhousing the water tanks and the cooling tower.

As shown in FIG. 9, a data center can be constructed with coolingmodules 910. In some embodiments, a cooling module 910 includes a heatexchanger, a chiller, a controller, pumps, wiring, valves and piping.The cooling module 910 contains the components in a housing that is upto 13.5 feet wide and 97 feet long, but can be smaller, such as lessthan 40 feet, less than 30 feet or less than 20 feet long. The coolingmodule 910 can also be narrower, such as less than about 12 feet, lessthan 10 feet or less than 8 feet wide. Specifically, the cooling module910 can be sized to be transportable over roads. The cooling module 910therefore can be assembled off-site, such as in a factory or othercontrolled environment, and transported to the data center location. Thecooling module 910 is then connected to the data center once in place.Because the cooling module 910 is assembled off-site, potentiallycomplex wiring and plumbing jobs can be eliminated from being performedon-site.

The cooling module 910 can be connected to a tank module and coolingtower assembly 920. The tank module can house the primary water storagetank and the second water storage tank. A cooling tower is then locatedproximate to the tank module. In some embodiments, a platform isconstructed over the tank module and the cooling tower is located on theplatform. The primary storage tank and secondary storage tank can eachhave a capacity of about 15,000 gallons and can have dimensions of about8 feet in diameter and 40 feet long, that is, in the shape of a longcylindrical tube. Because the tank module and cooling tower assembly 920is mechanically simple, it can be constructed on-site and connected tothe cooling module 910, such as by piping connected to the coolingmodule 910. As the data center grows in size and capacity, more coolingmodules 910 and tank module and cooling tower assemblies 920 can beadded. This modular system allows for more modules to be added asrequired.

A number of embodiments have been described. Nevertheless, it will beunderstood that various modifications may be made without departing fromthe spirit and scope of what is described. For example, the steps of theexemplary flow chart on FIG. 6 may be performed in other orders, somesteps may be removed, and other steps may be added. Accordingly, otherembodiments are within the scope of the following claims.

What is claimed is:
 1. A system for providing cooled air to electronicequipment in a data center, comprising: a cooling tower operable toreceive heated water and output cooled water; a water storage tankfluidly coupled to the cooling tower and storing the cooled waterreceived from the cooling tower; an air-to-water heat exchangerpositioned to receive heated air from a group of electronic devices; anda controller that monitors a current temperature of the water in thewater storage tank, wherein when detecting that the current temperatureof the water in the water storage tank is below a pre-determinedthreshold value, the controller routes the heated water received fromthe air-to-water heat exchanger to the water storage tank bypassing thecooling tower, while routing a mixture of the cooled water in the waterstorage tank and the heated water received from the air-to-waterexchanger back to the air-to-water exchanger, and based on detectingthat the current temperature of the water in the water storage tank isabove the pre-determined threshold value and a volume of water inanother water storage tank is above a threshold volume associated with apower usage of the data center, the controller routes water from thewater storage tank and water from the other water storage tank to theair-to-water heat exchanger, and based on detecting that the currenttemperature of the water in the water storage tank is above thepre-determined threshold value and the volume of water in the anotherwater storage tank is below the threshold volume associated with thepower usage of the data center, the controller routes a mixture ofchilled water circulated from a chiller with the cooled water from thewater storage tank to the air-to-water heat exchanger.
 2. The system ofclaim 1, wherein the water storage tank is configured to retain at least15,000 gallons of water.
 3. The system of claim 1, wherein the system isfree of a condenser-type chiller.
 4. The system of claim 1, furthercomprising a water-to-water heat exchanger fluidly coupled to the waterstorage tank and the air-to-water heat exchanger, wherein thewater-to-water heat exchanger keeps the water from the water storagetank isolated from the water in the air-to-water heat exchanger.
 5. Thesystem of claim 1, further comprising: a chiller; and a secondarystorage tank fluidly coupled to the chiller to retain cooled water fromthe chiller and to route the cooled water from the chiller to theair-to-water heat exchanger.
 6. The system of claim 5, wherein thesecondary storage tank includes a buffer tank and a thermal storagetank, wherein the buffer tank is fluidly coupled to the thermal storagetank.
 7. The system of claim 1, further comprising a water treatmentsystem for removing contaminants from water flowing through the system.8. The system of claim 1, further comprising: a module, comprising: ahousing, wherein the housing is no more than 13.5 feet wide and is nolonger than 97 feet; a water-to-water heat exchanger within the housing;and a chiller within the housing; and the controller within the housing,wherein the controller regulates a flow of water from the water-to-waterheat exchanger and the chiller to outside of the housing; and whereinthe water storage tank has a capacity of at least 10,000 gallons and isfluidly coupled to at least one of the chiller or the water-to-waterheat exchanger.
 9. The system of claim 1, wherein the pre-determinedthreshold value comprises a temperature range.
 10. A temperaturecontrolled data center comprising: a cooling tower operable to receiveheated water and output cooled water; a water storage tank fluidlycoupled to the cooling tower and storing the cooled water received fromthe cooling tower; an air-to-water heat exchanger positioned to receiveheated air from a group of electronic devices; a controller thatmonitors a current temperature of the water in the water storage tank,wherein when detecting that the current temperature of the water in thewater storage tank is below a pre-determined threshold value, thecontroller routes heated water received from the air-to-water heatexchanger to the water storage tank bypassing the cooling tower, whilerouting a mixture of the cooled water in the water storage tank and theheated water received from the air-to-water exchanger back to theair-to-water exchanger, and based on detecting that the currenttemperature of the water in the water storage tank is above thepre-determined threshold value and a volume of water in another waterstorage tank is above a threshold volume associated with a power usageof the data center, the controller routes water from the water storagetank and water from the other water storage tank to the air-to-waterheat exchanger, and based on detecting that the current temperature ofthe water in the water storage tank is above the pre-determinedthreshold value and the volume of water in the another water storagetank is below the threshold volume associated with the power usage ofthe data center, the controller routes a mixture of chilled watercirculated from a chiller with the cooled water from the water storagetank to the air-to-water heat exchanger; and a building housing thegroup of electronic devices, the electronic devices comprising computingsystems, wherein, when in operation, the computing systems raise thetemperature of air within the building, and water flowing through theair-to-water heat exchanger lowers the temperature of air within thebuilding.
 11. A method of providing cooled air to electronic equipment,comprising: allowing water in a cooling tower to cool throughevaporative cooling; flowing the cooled water from the cooling tower toa water storage tank and storing the cooled water from the cooling towerin the water storage tank; monitoring a current temperature of the waterin the water storage tank; and based on detecting that the currenttemperature of the water in the water storage tank is below apre-determined threshold value, routing heated water from anair-to-water heat exchanger to the water storage tank bypassing thecooling tower, while routing a mixture of the cooled water in the waterstorage tank and the heated water from the air-to-water exchanger backto the air-to-water exchanger; cooling, by the mixture of cooled andheated water routed to the air-to-water heat exchanger, air surroundingthe air-to-water heat exchanger that has been heated by a group ofelectronic devices; based on detecting that the current temperature ofthe water in the water storage tank is above the pre-determinedthreshold value and a volume of water in another water storage tank isabove a threshold volume associated with a power usage of the datacenter, routing water from the water storage tank and water from theother water storage tank to the air-to-water heat exchanger; and basedon detecting that the current temperature of the water in the waterstorage tank is above the pre-determined threshold value and the volumeof water in the another water storage tank is below the threshold volumeassociated with the power usage of the data center, routing a mixture ofchilled water circulated from a chiller with the cooled water from thewater storage tank to the air-to-water heat exchanger.
 12. The method ofclaim 11, further comprising: flowing water from one of the coolingtower or the water storage tank to a water treatment system; removingcontaminants from the water at the water treatment system; and returningtreated water to one of the cooling tower or the water storage tank. 13.A method of providing cooled air to electronic equipment, comprising:allowing water in a cooling tower to cool through evaporative cooling;flowing the cooled water from the cooling tower to a water storage tankand storing the cooled water from the cooling tower in the water storagetank; monitoring a current temperature of the water in the water storagetank; based on detecting that the current temperature of the water inthe water storage tank is below a pre-determined threshold value,routing heated water from a water-to-water heat exchanger to the waterstorage tank bypassing the cooling tower, while routing a mixture of thecooled water in the water storage tank and the heated water from thewater-to-water exchanger back to the water-to-water exchanger; based ondetecting that the current temperature of the water in the water storagetank is above the pre-determined threshold value and a volume of waterin another water storage tank is above a threshold volume associatedwith a power usage of the data center, routing water from the waterstorage tank and water from the other water storage tank to anair-to-water heat exchanger; based on detecting that the currenttemperature of the water in the water storage tank is above thepre-determined threshold value and the volume of water in the anotherwater storage tank is below the threshold volume associated with thepower usage of the data center, routing a mixture of chilled watercirculated from a chiller with the cooled water from the water storagetank to the air-to-water heat exchanger; cooling, by the mixture ofcooled and heated water routed to the water-to-water exchanger, heatedwater from the air-to-water heat exchanger; isolating the water flowingthrough the air-to-water heat exchanger from the water from the waterstorage tank; and cooling, with the water flowing through theair-to-water heat exchanger, air surrounding the air-to-water heatexchanger that has been heated by a group of electronic devices.